1. Field of the Invention
The present invention relates to a method and system for producing activated carbon. More particularly, the present invention relates to a method and system for producing activated carbon, in which cellulose acylate can be utilized as raw material, and the activated carbon can be produced with economized heat energy.
2. Description Related to the Prior Art
Polymer films have excellent optical transmittance and flexibility and are capable of forming thin and lightweight films. Owing to this, the polymer films are widely used as optical functional films. In particular, a cellulose acylate film formed of cellulose acylate and the like has toughness and low birefringence in addition to those properties. The film is used as a support of photo film or photosensitive material, and a protection film for a polarizing filter incorporated in a panel, namely, a liquid crystal display (LCD) whose market is recently expanding.
In a polarizing filter production process to produce polarizing filters, approximately 30% of the total amount of supplied films is discarded. The discarded films or waste films are rapidly increasing in accordance with rapid market expansion of the polarizing filters. However, reuse and recycle systems have not been developed for the waste films in comparison with a reuse system of wastepaper and a recycle resin forming system of waste plastics. Waste films are burned or disposed of in landfills at additional waste-processing expense.
However, reuse of the waste films has not been known with the viewpoint of recent environmental problems and saving of resources.
To reuse waste materials, their recycling as raw materials for newly producing film is conceived. Separation or isolation of cellulose acylates and polyvinyl alcohol from waste films is required. Furthermore, various additives are contained in waste materials of polarizing filters, as those must be contained polymer films as initial form of polarizing filters. It is extremely difficult to isolate the cellulose acylates and polyvinyl alcohol, namely to recover the cellulose acylates and polyvinyl alcohol selectively by removing additives from the waste films in the mixture. The cellulose acylates and polyvinyl alcohol will be unrecoverable as material for new films.
Paper, wood, and thermoset resins such as phenol resin become porous without liquefaction upon application of heat. JP-A 11-171524 discloses a method which reuses wastepaper such as old newspaper and the like as a raw material of activated carbon. JP-A 7-172808 discloses a method which reuses phenol resin-based wastes as raw materials of activated carbon. There is a known process of decomposing cellulose acylate by application of heat.
However, in many cases, carbonized materials generated by carbonization of waste materials do not have high absorptivity due to the above reasons. Accordingly, carbonized materials are used not as adsorbents, but mainly as soil improvement agents, fuels or the like.
According to the conventional knowledge, the thermoplastic resin does not become porous characteristically in carbonization, because of thermal decomposition with heat. Although it is well-known that cellulose acylate as thermoplastic resin decomposes when heated, a reaction mechanism of its carbonization has not been essentially found. There is no known method of producing activated carbon from waste material of polarizing filters which have increased industrially. Saving of heat energy is an important focus because heat energy of a very great amount is required for producing activated carbon.